Radiation detectors used in well-logging tools employ gas ionization to detect various types of radiation, such as neutron radiation, beta particle radiation, gamma particle radiation, or X-ray radiation. A gas ionization radiation detector includes a gas chamber filled with helium-3, for example. The gas chamber also includes a thin, axially extending wire forming an electrode that acts as the anode, which is suspended within a cylindrical housing that acts as a cathode and forms the gas chamber. When connected to an appropriate source of high voltage, the housing and the wire create an electric field within the chamber. This radiation detector operates on the principle that a charged particle that travels through the gas will interact with the helium-3 and produce ions and electrons (e.g., ionization), which will drift towards the anode and generate avalanches that produce further electrons and ions, which are detected at the anode. In this manner, the gas ionization radiation detector detects radiation that travels through the gas chamber.
These helium-3 radiation detectors are susceptible to mechanical especially at high temperatures, which is compounded in petroleum downhole applications when a downhole tool carrying the radiation detector is inserted within the borehole and available space is limited. The downhole environment includes high pressures, high temperatures, substantial mechanical vibrations and strong mechanical shocks. The elongate electrode forming the anode is made from a metal such as a thin tungsten wire, whereas the cylindrical housing forming the outer chamber wall, i.e., cathode, is made from another metal that has a different and higher coefficient of thermal expansion (TCE). As temperature increases in the downhole environment, this difference in TCE results in higher tensile stresses on the thin wire forming the anode until the wire breaks. Also, the wire is more likely to fail whenever any increase in temperature is accompanied by mechanical shocks or vibrations, as in the case of the downhole applications. Even if the wire does not break, the helium-3 radiation detector performance is diminished if the tension required at the wire is not maintained within an established operating range.